Time delay mechanism for machine gun



June 19, 1962 o. SYLVESTER ET AL 3, 3 ,3 5

TIME DELAY MECHANISM FOR MACHINE GUN Filed March 11, 1960 2 Sheets-Sheet 1 4I 6O 52 H '6 /IO I9 l8 II 8O ,2 1 28 27 59 I4 I? In?! \k I l 2 m I w77%% N 83 2 1 I A my k i 40 2I za 24 1 l5 LT 39 25 I00 I01 7o @71 0 59' FIG. 2 25 0| 32 FIG 5 sour SEARED TIME (Low RATE) SEAR RELEASE OPEN P$|TION B2| SEARED 5 POSITION E U 3 HIGH RATE OF FIRE a 5 z LOW RATE 8 OF FIRE 1 b g F 6 CLOSED POSITION TIME I INVENTORS 39 PATH/CK E. SWEENEY /O /D s v TER EE FW gmzg 5y m FIG. 4 25 A TTORNEY June 19, 1962 D. SYLVESTER ET AL 3,039,365

TIME DELAY MECHANISM FOR MACHINE GUN Filed March 11, 1960 2 Sheets-Sheet 2 %Ffi 52 76 r f %m 53 g: 11%;: 5 so FIG 7 s F IG. 8

IN V EN TORS FMTR/CK E. SWEENEY DAV/0 SYLVESTER I ATTORNEY 3,039,365 TIME DELAY MECHANISM FOR MACHINE GUN David Sylvester and Patrick E. Sweeney, Baltimore County, Md., assignors to Aircraft Armaments, Inc., Cockeysville, Md., a corporation of Maryland Filed Mar. 11, 1960, Ser. No. 14,376 3 Claims. (c1. 89-130) This invention relates to automatic machine guns and, more particularly, to an automatic machine gun having a dual rate of fire.

Guns of the class described generally include a bolt mounted for cyclical reciprocation between a closed-bolt position adjacent the chamber and an open bolt position remote from the chamber. The cycle starts when the bolt is at closed-bolt posit-ion closing the chamber with firing of the cartridge therein. After the cartridge is fired, the bolt recoils from the closed-bolt position to permit the spent cartridge to be extracted and a new cartridge to be chambered. After buffering at open-bolt position, the bolt counter-recoils to closed-bolt position whereupon the cycle is repeated. The time required for the bolt to complete the above described cycle determines the rate at which the gun fires. With proper design of the bolt and other appurtenances associated with the machine gun, the cycle time can be made very small to achieve a very high rate of fire. For various reasons, it would be desirable if the machine gun could easily be adjusted to switch from such high rate of fire to a lower rate of fire and back again.

It is an object of this invention to selectively reduce the firing rate of a machine gun of the class described by selectively causing the bolt to dwell at some position in its cycle.

It is a further object of this invention to control the firing rate of a machine gun of the class described by utilizing cyclical movement of the bolt to initiate a device that introduces a dwell in the bolt cycle.

It is a further object of this invention to control the time required for a reciprocating element to complete a cycle without appreciably changing the instantaneous speed of the element at any given position in the cycle.

In the drawing:

FIGURE 1 is a cross-sectional view of a machine gun in which the present invention is incorporated showing the relationship between movable elements with the bolt seared prior to firing. 7

FIGURE 2 is a view similar to FIGURE 1, but show ing the relationship between various elements just after the bolt is unseared.

FIGURE 3 is a view similar to FIGURE 1, but showing the recoil of the bolt assembly positioning the sear so that it will engage the bolt assembly on its counter-recoil stroke.

FIGURE 4 is a view similar to FIGURE 3, but showing the bolt assembly temporarily seared.

FIGURE 5 is a top-sectional view of the gun showing the bolt assembly locked to the barrel assembly.

FIGURE 6 is a displacement-time diagram of the bolt assembly for the high and low rates of fire.

FIGURE 7 is an enlarged view of the time-delay mechanism shown in FIGURE 1. 7

FIGURE 8 is a view taken along the line 88 of FIGURE 7.

FIGURE 9 is an exploded view of the elements making up a part of the time-delay mechanism.

Referring now to the drawing, reference numeral 10 denotes a machine gun incorporating the present invention. Receiver 11 constitutes 'a rigid housing or support for barrel assembly 12 which includes barrel 13 rigidly connected to barrel extension 14. Barrel 13 is provided with two bearing supports slideably m-ounted'in the forward end of receiver 11, but only rear support 15 is shown 3,@3,3fi5 Patented June 19,1962

in FIGURE 1. When the barrel assembly is in battery position, the rear face of support 15 is in contact with the forward cam face of accelerator 16 which is pivotally mounted on receiver 11. Barrel 13 is chambered at .17 in order to receive cartridge 18 held above and behind the chamber in link 19 on ammunition tray 20.

Barrel extension 14 has spaced elongated legs extending rearwardly (one of which is shown at 21) which slideably engage tracks inside the receiver so that the barrel extension is free to reciprocate. Barrel-return spring assembly 22 projects from the rear and is engageable with the solenoid frame when the gun is fired as will be described later. The inner wall of each leg 21 has extractor groove 23 and bolt groove 24 therein. The forward end of the barrel extension to which the barrel is fastened has keeper notches therein. At battery position, the bolt locks project outwardly into the notches and when the round is fired, the barrel extension receives the firing loads through the bolt locks.

Bolt assembly 25 includes bolt slide 26 and bolt block 27. Bolt block 27 is mounted in the upper portion of the bolt slide with along extension 28 of the bolt block extending rearwardly through recess 29 in the upper rear portion of the slide. The block is fastened in the slide by a pin attached to the slide which passes through a slot in the block. This arrangement permits a limited relative movement between the block and slide to provide the locking and unlocking action to be described. Firing pin 29 rigidly mounted in the upper rear portion of the bolt slide projects through and is slideable in aperture 30 in the bolt block. A pair of bolt locks 31 are pivotally mounted on bolt block 27. The bolt locking operation occurs as the bolt assembly approaches its closed position adj acent to the chamber. Forward movement of the slide is halted as will be later described when locks 31 are adjacent notches 32 in the barrel extension. Relative motion between the slide and the block can now occur as forward face 33 on the upper portion of the slide that contains the firing pin acts against inner sides 34 of the locks and earns them outwardly into keeper notches 32. During such relative movement firing pin 29 slides in aperture 30 (simultaneously with seating of the locks) until the fin'ng pin projects forwardly of the block into contact with a cartridge. Such contact fires the cartridge. It should be noted that the bearing of locks 31 on the inner grooved faces 35 of legs 21 prevent relative movement between the block and slide at all positions of the block except when the latter is positioned such that the locks are aligned with the keeper notches.

The bolt unlocking operation occurs as the. bolt slide moves rearwardly relative to the bolt block. Locks 31 have lugs 36 rigid therewith that engage cam grooves 37 in the upper surface 38 of the bolt slide. Cam. grooves 37 are so shaped that a small amount of rearward movement of the slide relative to the block can occur before the cam grooves cam the bolt locks inwardly out of the keeper notches whereupon the bolt assembly is freed from the barrel extension and is able to move relative thereto as a unit.

The bolt buffer assembly comprises ,a spring rod 39 rigidly mounted in receiver 11 and passing through buffer cylinder 40 on slide 26, and buffer spring 10%). Bolt driving spring 101 fits over rod 39 into engagement with the forward inner face of cylinder 40.

The bolt sear assembly 41 includes a sear 42 pivotally mounted in a frame attached to receiver 11. Sear spring 43 urges the sear into an effective position where it is engageable in sear notch 44 in bolt slide 26 when the bolt assembly is at open-bolt position. When sear 42 is in notch 44-, the bolt assembly is maintained in the position shown in FIGURE 1 against the action of bolt driving spring 101 which urges the bolt assembly toward closedbolt position adjacent chamber 17. Sear crank is pivotally mounted on receiver 11 and has arms which project forwardly beneath a lip on the sear. Rotation of sear crank 45 in a counterclockwise direction as seen in FIGURE 1 causes sear 42 to pivot against the action of spring 43 to an ineffective position out of engagement with sear notch 44 as best seen in FIGURE 2. Driving spring 161 is thus permitted to return the bolt assembly from opento closed-bolt position.

Back plate assembly 46 is mounted on the rear end of receiver 11, and includes solenoid housing 47 in which solenoid 48 is inserted. Armature 49 is slideably mounted for reciprocation relative to solenoid 48, and has armature extension 50 extending rearwardly into abutting contact with trigger cap 51. Cap 51 is slideably mounted in a cavity in manual trigger 52 and is urged into contact with extension 50 by trigger spring 53. Trigger 52 is pivotally mounted on shaft 54 attached to the back plate assembly. Armature 49 is hollow and has solenoid plunger 55 rigidly pinned thereto so that both elements move as a unit. Plunger spring 56 surrounds plunger 55 and has one end bearing on housing 47 and the other end bearing on armature 49 such that the plunger is urged rearwardly toward its inoperative position. Plunger head 57 on the forward end of plunger 55 contacts sear crank 45 and when the solenoid is not energized, the trigger, plunger and sear are in the relative positions indicated in FIGURE 1. Plunger 55 attached to armature 49 and sear crank 45 constitute means for actuating sear 42.

With the gun loaded and the bolt seared in open position as shown in FIGURE 1, firing is initiated by either energizing solenoid 48 or depressing the manual trigger 52. Operation of the solenoid by energizing the same causes the sear actuator means, comprising plunger 55 and crank 45, to overcome spring 43 and move forward to operative position as shown in FIGURE 2. The energized solenoid releasably maintains the sear actuator means at operative position so that sear 42 is maintained out of engagement with notch 44 in bolt assembly 25 when the latter moves to open position. As abov indicated, firing can alternatively be accomplished by depressing trigger 52, In such case, operation of trigger 52 by depressing the same urges cap 51 forwardly through the medium of spring 53. Such forward movement of cap 51 causes the sear actuator means to overcome spring 43 and move forward to operative position in the same way that operation of solenoid 48 accomplishes this result. Thus, solenoid 48 and trigger 52 (together with cap 51 and spring 53) constitute trigger means which are manually operable to releasably maintain the sear actuator means at operative position. During operation of said trigger means, sear 42 is releasably maintained out of engagement with bolt assembly 25 when the latter moves to open position. The term releasably is used to describe the manner in which the sear actuator means is maintained at operative position and the sear is maintained out of engagement with the bolt assembly because the sear actuator means can move out of operative position during operation of the solenoid and the trigger. Movement of the sear actuator means can occur during operation of the trigger means by applying a force to the sear actuator means which is opposite to the force applied by the magnetic field of the energized solenoid on armature 48 and by the spring 53. The means for applying such opposite force is described hereinafter.

Since operation of the trigger means maintains the sear out of engagement with the bolt assembly, bolt driving spring 101 is effective to move the bolt assembly from open to closed position. During the forward movement of the bolt assembly stripper 58 (FIGURE 1) contacts the base of cartridge 18 and forces the cartridge out of the link. As the cartridge is pushed forwardly, the projectile end is cammed downwardly by the chambering ramp 1-1 on the receiver and the base of the cartridge slides down the forward face of the bolt block until its extraction groove is engaged by bottom extractor 59 (FIGURE 1) which is cammed upwardly by groove 23. Forward movement of the bolt block is stopped by chambering of the cartridge in chamber 17. As above described, forward movement of the bolt slide continues and the bolt locks are camrned into the keeper notches as the firing pin extends through the aperture in the bolt block until it strikes and fires the cartridge primer. This is the closed-bolt position of the bolt assembly.

Upon firing, the barrel assembly and the bolt assembly, which is locked to the barrel extension, begin the recoil stroke as a single unit. The recoil is opposed by the barrel return springs 22, bolt driving spring 101, and accelerator 16, which is biased into contact with bearing 15. Just as bolt locking and firing are simultaneous, so bolt unlocking and acceleration are simultaneous. The recoiling barrel contacts the accelerator, and portion 60" of the accelerator contacts cylinder 40 of the bolt assembly. The design is such that initial accelerator movement does not cause any relative movement between the slide and the barrel extension and the bolt assembly remains locked to the barrel extension. After a short recoil displacement of the barrel assembly, the gas pressure in the gun bore decreases, and the bolt assembly is unlocked from the barrel extension. This occurs because after the initial recoil displacement, portion 60" of accelerator v16 imparts a high acceleration to the bolt slide, and the bolt slide begins to move relative to the block. During initial relative movement, cam grooves 37 acting on pins 36 on the ends of locks 31, cams the locks out of notches 34 thereby freeing the bolt assembly from the barrel extension. During further relative movement, the pin on the slide moves through the slot in extension 28 of the block until it contacts the rearmost end whereupon the slide pulls the block on the barrel extension toward open-bolt position.

As the bolt assembly is unlocked and recoils from its closed position on the barrel extension, extractor 59 withdraws the spent cartridge from chamber 17 so that as extractor 59 is cammed downwardly by groove 23, the cartridge case is ejected by mechanism not shown. The bolt assembly continues toward open-bolt position oompressing charging spring 1&1, and the barrel assembly is buttered by barrel return springs 22 and begins to return to battery position. As the barrel assembly approaches battery position, the bolt assembly is buffered by spring at open-bolt position. Buffer spring 100 and bolt charging spring 101 immediately drive the bolt assembly toward closed position. The above described action of the gun repeats itself as long as plunger 55 maintains sear 42 out of notch 44. When the firing solenoid is deenergized or the manual trigger is released, as the case may be, plunger 55 under the influence of spring 56 moves to the inoperative position shown in FIGURE 1 and sear spring 43 returns sear 42 to its effective position. Now, when the bolt assembly approaches open position, sear 42 is cammed out of the way by the upper rear portion of the bolt slide. After the bolt slide passes beneath sear 42, spring 43 immediately returns the sear to its eifective position engaged with notch 44. In this manner, the sear is responsive to movement of the bolt assembly to open position for engaging and retaining the latter at open position against the action of deflected charging spring 101. Thus, when plunger 55 is at inoperative position, it eifects engagement of sear 42 with the bolt assembly whereby the sear prevents the charging spring from moving the bolt assembly from open to closed position.

Reference is now made to FIGURE 6, which shows the bolt time-displacement curve for the gun. At the maximum displacement position relative to the chamber, the bolt assembly has zero velocity relative to the barrel extension, since this is the position at which the bolt as sembly changes direction of movement. The seared po sition of the bolt assembly is only slightly removed from the maximum displacement position and provides for positive searing of the bolt assembly when plunger is moved to inoperative position. However, since the distance from the maximum displacement position to the chamber is substantially the same as the distance from the seared position to the chamber, the term open-bolt position is used to denote both the maximum displacement position and the seared bolt position. It should be understood, therefore, that searing of the bolt assembly occurs when it moves to open-bolt position.

To achieve a lower rate of fire, time delay mechanism 58' is employed to introduce a dwellin the movement of the bolt assembly at the open-bolt position. The function of this mechanism is to hold solenoid plunger 55 at its inoperative position for a fixed periodof .time when the bolt assembly is at open position such that sear 42 retains the bolt assembly at the open position for a fixed period of time. At the end of the fixed period of time, the mechanism releases plunger 55 which can move again to its operative position causing sear 42 to release the bolt assembly, which then begins the cycle previously described. The components of mechanism 58' are mounted on back plate assembly 46 and comprise time delay drum 59, yoke 60, and selector assembly 61.

Drum 59' is a cam rotatably mounted on shaft 62 which is rigidly attached to the back plate by lugs 63 and nut 64. The axis about which the drum rotates is normal to the path of travel of the bolt assembly. Engaged in notch 65 on one end of shaft 62 is one end of torsion spring 66 which surrounds the shaft. The other end of spring 66 is engaged in notch 67 in drum 59 as shown best in FIGURE 8. This spring urges the drum in a counterclockwise direction as seen in FIGURE 7. A stop 68 rigidly secured to the back plate assembly is engaged against face 69 on the drum and serves to retain the latter against the action of spring 66 in an initial angular position.

Drum 59' is essentially cylindrical in shape, and has semi-circular groove 70 extending peripherally around the drum in the middle thereof. Longitudinal flats 71 are formed on the drum such that bearing surface 72 protrudes above the flats as seen in FIGURE 9. Rollers 73 mounted in axles 74 in each leg 75 of yoke 60 are engaged with flats 71. Yoke 60 is pivotally mounted on pin 76 remote from the rollers and has opening 77 adjacent the pivoted end. Extension 50 projects through opening 77 as shown in FIGURE 7. Pin 78 rigidly connected to extension 50 is spaced from yoke 60 when plunger 55 is at its inoperative position and drum 59 is at its initial angular position. When plunger 55 moves to its operative position upon energization of solenoid 48, or depression of trigger 52, pin 78 is in substantial contact with arms 79 of yoke 60.

Selector assembly 61 includes striker pin 80 having one end rotatably mounted in bearing 81 in back plate assembly 46, and the other end reduced as at 82. Striker tube 83 is slideably mounted on pin 86 with striker return spring 84 bearing against the forward end of tube 83 and against face 84 of pin 80. Connector pin 85 is rigidly connected to pin 80 and extends through slots 86 in tube 83 such that tube 83 is slideable on pin 80, and is caused to rotate when pin 80 is rotated by selector lever 87 keyed to pin 80. The foiward end of tube 83 has a semicircular contactor portion 88 which can be moved into or out of the recoil path of the bolt assembly depending upon location of rate selector lever 87. The rear end 89 of tube 83 is in contact with bearing surface 72 when drum 59' is in its initial angular position regardless of the position of selector lever 87. This contact also holds drum 59 in its initial angular position. FIGURES 1 through 4, 6 and 7 show the selector lever at low rate with portion 88 shown on FIGURES 7 and 9 directly in the recoil path of extension 23 on the bolt assembly.

With the selector lever at low rate, energizing the solenoid moves plunger 55 from the inoperative position of FIGURE 1 to the operative position of FIGURE 2 with pin 78 into engagement with arms 79 of yoke 60. The forward movement of the bolt assembly is as previously described. When the bolt assembly recoils to open position, it engages portion 88 of tube 83 causing the tube to slide on pin 80 as shown in FIGURE 3. The engagement causes end 89 to contact surface 72 and impart rotation to drum 59' away from its initial angular position against the action of spring 66. Such rotation causes yoke 60 to pivot as rollers 73 ride from flats 71 to the curved portion of drum 59' thereby moving plunger 55 from operative to inoperative position against the effort of the energized solenoid. At the inoperative position, the plunger eifects engagement of scar 42 with notch 44 after the bolt assembly is buffered and begins its counter recoil stroke whereby the sear prevents the charging spring from moving the bolt assembly from open to closed position. The bolt remains seared as long as drum 59 is away from its initial angular position.

Rotation of the drum proceeds against the increasing resistance of the torsion spring until shoulder 69' on the drum contacts stop 68. Such contact stops rotation of the drum whereupon the torsion spring returns the drum to its initial angular position. This is shown in FIGURE 4. During the time interval that the drum is away from its initial angular position, yoke 60 holds plunger 55 at inoperative position against the effort of the energized solenoid, or against the effort of spring 53 if trigger 52 is depressed. In the above described manner, the bolt assembly is caused to dwell at the beginning of its counterrecoil stroke. However, the bolt assembly recoils at the same instantaneous speed regardless of whether a dwell is introduced in the cycle at open-bolt position. This is extremely important when recoil movement of the bolt is used to energize a gun mechanism, since the energy available to the mechanism does not change when the rate of fire is changed. During the low rate of fire the bolt assembly counter recoils at a slightly lower instantaneous speed (indicated by the slightly decreased slope of the dashed portion of the curve of FIGURE 6 in comparison to the solid portion of the curve) since the counter-recoil etfect of buffer spring is absorbed by sear 42. However, the instantaneous speed of the bolt assembly at a given position of displacement is substantially the same regardless of the rate at which the gun is firing.

To convert the gun from a low rate of fire to a high rate, lever 87 is rotated until contactor portion 88 is out of the recoil path of extension 28 when the latter moves to open position. The sequence of operation is as previously described except that when the bolt assembly recoils to open position, extension 28 clears portion 88, plunger 55 holds sear 42 out of notch 44 whereby charging spring 101 is eifective to move the bolt assembly from open to closed position immediately after the bolt assembly arrives at open position. In this manner, the firing rate is easily changed from a high rate to a low rate by merely rotating the selector knob to place portion 83 either in or out of the path of the bolt assembly.

Those skilled in the art will now appreciate that this invention provides a mechanism by which the firing rate of a machine gun can easily be controlled.

What is claimed is:

1. In a machine gun, the combination of a barrel assembly mounted in a receiver, said barrel assembly having a chamber for receiving a cartridge, a bolt assembly movably mounted on said barrel assembly between a closed position adjacent said chamber and an open position spaced from said chamber, movement of said bolt assembly to closed position causing said cartridge to be fired and said bolt assembly to recoil to open position, a boltdriving spring deflected by movement of said bolt assembly to open position for urging the latter toward closed position, a movable sear, biasing means urging said sear toward an effective position engaged with the bolt assembly when the latter is at open position for retaining the bolt means is moved out of operative position and remaining at its eifective position for said fixed time whereby said element dwells at said terminal point for said fixed time.

References Cited in the file of this patent UNITED STATES PATENTS 1,573,655 Sutter Feb. 16, 1926 50 1,771,132 Mascarucci July 22, 1930 2,116,140 Browning May 3, 1938 2,791,942 Fletcher May 14, 1957 with earls and to en position d cam havut of operative mally efiective losed position, spring f said trigger means or means at operative 5 1 .3e e ..e.. .n 1 Y1 1 V t 1. 3 2 .0 5 1 3 U P 3 d a. 1%.... f. 3 J U: rt 5 I r P. N l O l 1 1 IE 1 J M f n": 1 wfm ma ..1 0 1+ 5 M K541 b O l .1 i 3 3 .a .r I 3 d n 3 D. h b w .P e d W .2... .6 .a .1 .1 F. S g H 1 r 3 a n .9. 6 Q .wb .hu .r 0 .1 l 3 a d .8. .I it 3 .P E C .l 3 i l f 1 f S 1 U f I we 2 1 O r. .1 D 0 S l h :1 D i 2 v. mw s e t t t n 1 g 3 7: t. C l .1 fi .1 .1 U U Ll. t n f d E U o. n .1 l D GU J .l is .1 n E l V :0. C u r. 3 B U .1 3 6. n C U .1 .:1.. 1 r M 1 3 U t 1 1 h I e .r Z .1 D n S l t. .3 C o 1 l .1 .1 .a 2.. l .5 a P 3 d C C o: In 3 S t n 1 J: 1 H t 1 m I n )4 ,2 E n fieetive position, trigger means 4 5621 zcttatcr means ha I1g an ope! all at its; efhzive hereby s2id lzclt ass=nb is. aimed a cp:1 i

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